1. Field of the Invention
The present invention relates to a polypropylene resin composition and to a formed article comprising the same. In particular, the invention relates to a polypropylene resin composition superior in rigidity and impact resistance and also superior in thermal aging resistance and to a formed article comprising the same.
2. Description of the Related Art
Polypropylene resins are widely used in a wide variety of applications such as automotive interior or exterior materials, materials for home electrical products, containers and convenience goods because they are materials superior in mechanical properties such as rigidity and impact resistance. One of known approaches for improving mechanical properties of polypropylene resins is blending of a nucleating agent.
For example, Plastic Databook (§9.7 “Nucleating Agent” pp. 978–980, published by Kogyo Chosakai Publishing Co., Ltd.) discloses nucleating agents. For example, disclosed are nucleating agents such as inorganic nucleating agents, e.g. talc, and metal salt type nucleating agents, e.g. metal salts of carboxylic acids and phosphate type metal salts. In addition, the book discloses injection moldings of polypropylene containing such a nucleating agent as well.
JP,A 63-125551 discloses, as a propylene polymer composition which does not corrode metal molds to damage it and which has improved rigidity and transparency, a propylene polymer composition comprising 100 parts by weight of a propylene polymer containing Mg and halogen as a polymerization catalyst residue, from 0.03 to 0.5 part by weight of an aluminum salt of p-tert-butylbenzoic acid and from 0.01 to 0.5 part by weight of at least one kind of substance selected from salts made up of a metal of Group I of the periodic table or zinc with a higher aliphatic carboxylic acid and hydrotalcites.
However, formed articles of the polypropylene resin containing a nucleating agent disclosed in the above-cited reference may be deteriorated with respect to impact resistance evaluated by falling weight impact strength and the like even if they have improved rigidities. Therefore, improvement in balance between rigidity and impact resistance has been awaited.
Furthermore, since polypropylene resins may be used under conditions of high temperatures not higher than their melting points for a long period of time, materials mechanical characteristics of which no not deteriorate very much during their long time use, in other words, materials superior in thermal aging resistance in their long time use have been awaited.